1. Field of the Invention
The present invention relates to data storage and retrieval generally and more particularly to a method and system for virtualization switch failover.
2. Description of the Related Art
Information drives business. Companies today rely to an unprecedented extent on online, frequently accessed, constantly changing data to run their businesses. Unplanned events that inhibit the availability of this data can seriously damage business operations. Additionally, any permanent data loss, from natural disaster or any other source, will likely have serious negative consequences for the continued viability of a business. Therefore, when disaster strikes, companies must be prepared to eliminate or minimize data loss, and recover quickly with useable data.
Storage virtualization is one technique which is used to simplify the storage and provision of data from the perspective of application host data processing systems and users. Storage virtualization is the application of virtualization to storage services or devices for the purpose of aggregating, hiding complexity or adding new capabilities to lower level storage resources. Using storage virtualization, the internal function of a storage (sub) system(s) or service(s) are abstracted, hidden, or isolated from applications, application host data processing systems, or general network resources for the purpose of enabling application and network-independent management of storage or data. Storage can be virtualized simultaneously in multiple layers of a system, and storage virtualization may be provided at the application host, network interconnect, or storage device level.
Where storage virtualization is implemented with a storage area network (SAN), interconnect there is a one to one correspondence between each host target identifier (e.g., logical device name, virtual LUN, or the like) used by an application host and unique interconnect device identifier (e.g., a Fibre Channel world wide port name and/or world wide node name) used within the storage network interconnect. Consequently, failover between multiple interconnect elements or devices (e.g., switches) or paths may result in the alteration of the unique interconnect device identifier (ID) associated with a given host target identifier when an interconnect element or device becomes unavailable due to failure or disconnection.
Where storage virtualization is provided at the application host level, the unique interconnect device identifier to host target identifier mapping may be updated using existing storage virtualization facilities. Alternatively, (e.g., where storage virtualization is provided at the network interconnect level by one or more virtualization switches) specialized dynamic multipathing (DMP) facilities at each application host are used to failover from one interconnect element to another. Such DMP facilities may operate with multiple storage network interconnect connection points (e.g., host bus adapters, network interface cards, or the like) or a single connection point.
The use of DMP facilities for interconnect element failover suffers from number of drawbacks. Such DMP facilities increase the processing and storage burden already placed on application hosts and require data concerning specific storage device commands, failover procedures, or the like to be available at an application host in contradiction with the aims of network interconnect-based storage virtualization. Additionally, if the failover of a storage network interconnect element (and the resultant unique interconnect device identifier change) is visible to an application host, every application of that application host must be reconfigured to use a new host target identifier because of the one to one correspondence required between host target and unique interconnect device identifiers, thus causing additional application errors and/or processing delay.